Grain-oriented electrical steel sheet and manufacturing method therefor

Abstract

This grain-oriented electrical steel sheet includes, on the surface, a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction. When, on said surface, a square evaluation region having a side length of 50 mm and having one side parallel to the rolling direction is set and when virtual lines which are parallel to the rolling direction and which each have a length of 50 mm are set at 5 mm intervals in a direction perpendicular to the rolling direction inside the evaluation region, the grain-oriented electrical steel sheet is configured such that, in at least one of the virtual lines, the maximum value of intervals in the rolling direction between adjacent intersections of a plurality of intersections between the virtual line and the plurality of magnetic domain control processing lines is greater than 20 mm, the average value of magnetic domain widths measured along the virtual line is 600 μm or less, and the plurality of magnetic domain control processing lines are tensile stress introduction lines into which tensile stress of 40 MPa or more is introduced.

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. This application claims priority based on Japanese Patent Application No. 2023-166093, filed on September 27, 2023, the contents of which are incorporated herein by reference.

[0002] Grain-oriented electrical steel sheets are steel sheets containing 7 mass% or less of Si and having a secondary recrystallization texture in which secondary recrystallized grains are concentrated in the {110}<001> orientation (Goss orientation), with the easy axis of magnetization <001> oriented in the rolling direction. Grain-oriented electrical steel sheets are mainly used as iron cores for power transformers. Reduction of energy loss (iron loss) is required for grain-oriented electrical steel sheets.

[0003] A technique for narrowing the magnetic domain width of grain-oriented electrical steel sheets (magnetic domain refinement technique by magnetic domain control treatment) has long been known to reduce iron loss. The magnetic domain width can be narrowed by irradiating the surface of the grain-oriented electrical steel sheet with a laser or electron beam in a direction intersecting the rolling direction to introduce thermal strain. The magnetic domain width can also be narrowed by forming grooves in the surface of the grain-oriented electrical steel sheet in a direction intersecting the rolling direction. Groove formation methods include laser or electron beam irradiation, mechanical processing such as gear machining, and chemical processing such as etching.

[0004] In recent years, various improved techniques relating to magnetic domain refinement have been proposed in order to provide grain-oriented electrical steel sheets with good iron loss characteristics (see, for example, Patent Documents 1 to 3).

[0005] Japanese Patent Publication No. 2012-57219 Japanese Patent Publication No. 2012-12664 Japanese Patent Publication No. 2012-57218

[0006] When magnetic domain control treatment is applied to grain-oriented electrical steel sheet, the magnetostriction characteristics of the grain-oriented electrical steel sheet change due to the closure magnetic domains. This causes the noise characteristics of the grain-oriented electrical steel sheet to deteriorate. The noise characteristics refer to the level of noise generated by electrical products (e.g., transformers, motors, etc.) manufactured using grain-oriented electrical steel sheet as a material. Magnetostriction is a phenomenon in which the external shape of a ferromagnetic material is slightly deformed when it is magnetized. When grain-oriented electrical steel sheet is excited with an alternating current, the magnitude of magnetostriction changes with the change in the strength of the magnetization, causing vibration. The magnitude of this magnetostriction is 10 －６ Although it is only on the order of magnitude, this magnetostriction generates vibrations in the iron core, which then propagate to external structures such as transformer tanks and cause noise. While magnetic domain control treatment is effective in reducing the iron loss of grain-oriented electrical steel sheets, it also worsens their noise characteristics. In recent years, there has been an increasing demand for grain-oriented electrical steel sheets to not only reduce iron loss, but also reduce noise. However, no magnetic domain refining technology has been proposed to date that can adequately achieve both low noise and low iron loss.

[0007] The present disclosure aims to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces little noise when used in electrical products (excellent noise characteristics), and a method for manufacturing the same.

[0008] The present inventors have investigated methods for reducing iron loss while suppressing deterioration of noise characteristics, and have found that by widening the intervals of magnetic domain control treatment in at least some specific regions when performing magnetic domain control treatment using tensile stress, it is possible to obtain a grain-oriented electrical steel sheet with low iron loss and excellent noise characteristics.

[0009] The present disclosure has been made in light of the above findings. The gist of the present disclosure is as follows: [1] A grain-oriented electrical steel sheet according to one embodiment of the present disclosure includes, on a surface thereof, a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction, and a square evaluation area is set on the surface, with one side 50 mm long and one side parallel to the rolling direction, and virtual lines 50 mm long and parallel to the rolling direction are set within the evaluation area at 5 mm intervals in a direction perpendicular to the rolling direction, where, for at least one of the virtual lines, among a plurality of intersections between the virtual line and the plurality of magnetic domain control treatment lines, the maximum distance in the rolling direction between adjacent intersections exceeds 20 mm, and the average magnetic domain width measured along the virtual line is 600 μm or less, and the plurality of magnetic domain control treatment lines are tensile stress introduction lines into which a tensile stress of 40 MPa or more has been introduced. [2] In the grain-oriented electrical steel sheet according to [1], the average value of the magnetic domain widths measured along the imaginary lines may be 500 μm or less. [3] In the grain-oriented electrical steel sheet according to [1], the average value of the magnetic domain widths measured along the imaginary lines may be 600 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm. [4] In the grain-oriented electrical steel sheet according to [3], the average value of the magnetic domain widths measured along the imaginary lines may be 500 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm. [5] A grain-oriented electrical steel sheet according to another aspect of the present disclosure includes, on a surface thereof, a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction, and a square evaluation area is set on the surface, with one side 50 mm long and one side parallel to the rolling direction, and further, within the evaluation area, imaginary lines parallel to the rolling direction and 50 mm long are set at 5 mm intervals in a direction perpendicular to the rolling direction, wherein, for at least one of the imaginary lines, among a plurality of intersections between the imaginary line and the plurality of magnetic domain control treatment lines, the maximum value of the distance in the rolling direction between adjacent intersections exceeds 20 mm, and the maximum value of the magnetic domain width measured along the imaginary line is 1200 μm or less.[6] In the grain-oriented electrical steel sheet according to [5], the maximum value of the magnetic domain width measured along the imaginary line may be 800 μm or less. [7] In the grain-oriented electrical steel sheet according to [5], the maximum value of the magnetic domain width measured along the imaginary line may be 1200 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm. [8] In the grain-oriented electrical steel sheet according to [7], the maximum value of the magnetic domain width measured along the imaginary line may be 800 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm. [9] In the grain-oriented electrical steel sheet according to any of [1] to [8], the multiple magnetic domain control treatment lines may be thermally strained.

[10] In the grain-oriented electrical steel sheet according to [9], the maximum value of the tensile stress introduced by the thermal strain in the magnetic domain control treatment line may be non-uniform at each measurement point of the tensile stress.

[11] In the grain-oriented electrical steel sheet according to

[10] , each of the multiple intersections of the virtual line and the multiple magnetic domain control treatment lines is defined as a magnetic domain refinement point, and the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points, is defined as TS. ｍ , the TS ｍ The variance of σ(TS ｍ ) ２ Then, σ(TS ｍ ) ２

[12] The grain-oriented electrical steel sheet according to

[10] may be characterized in that, when each of a plurality of intersections between the virtual line and the plurality of magnetic domain control treatment lines is defined as a magnetic domain refinement point, the arithmetic mean value of the maximum values ​​of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is defined as TS ｍ（β≧２） When this is done, TS ｍ（β＜２） >TS ｍ（β≧２）

[13] The grain-oriented electrical steel sheet according to

[11] may be characterized in that the arithmetic mean value of the maximum values ​​of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is defined as TS ｍ（β≧２） When this is done, TS ｍ（β＜２） >TS ｍ（β≧２）

[14] A method for producing a grain-oriented electrical steel sheet according to another aspect of the present disclosure is the method for producing a grain-oriented electrical steel sheet according to any one of [1] to [8], comprising: a magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electrical steel sheet; a region identification step of identifying regions in the grain-oriented electrical steel sheet where a magnetic domain width exceeds 500 μm based on the magnetic domain image acquired in the magnetic domain image acquisition step; and a magnetic domain control treatment line forming step of forming magnetic domain control treatment lines on the surface of the grain-oriented electrical steel sheet after the region identification step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment lines are formed in the regions where the magnetic domain width exceeds 500 μm.

[15] In the method for producing a grain-oriented electrical steel sheet according to

[14] , the magnetic domain control treatment line forming step may form the magnetic domain control treatment lines by irradiation with a laser or an electron beam.

[0010] According to the above aspects of the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces little noise when made into an electrical product (excellent noise characteristics), and a method for manufacturing the same.

[0011] 3C is a schematic diagram illustrating a method for extracting a plurality of partial regions from a magnetic domain image of a grain-oriented electrical steel sheet. FIG. 3D is a schematic diagram illustrating a plurality of partial Fourier images obtained by performing a two-dimensional Fourier transform on each of a plurality of partial regions extracted from a magnetic domain image of a grain-oriented electrical steel sheet. FIG. 3E is a schematic cross-sectional view of a grain-oriented electrical steel sheet in which magnetic domain control treatment lines are thermally strained. FIG. 3F is a schematic plan view illustrating a method for measuring magnetic domain control strength at an intersection of a magnetic domain control treatment line and a virtual line. 10 is a graph showing the relationship between the magnetic domain width and the magnetic domain control saturation strength, and the relationship between the β angle and the magnetic domain control saturation strength.

[0012] 1A , a grain-oriented electrical steel sheet 1 according to the present embodiment includes, on its surface, a plurality of magnetic domain control treatment lines 11 extending in a direction intersecting the rolling direction RD, and a square evaluation area is set on the surface, with one side 50 mm long and one side parallel to the rolling direction RD. Furthermore, within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction RD, are set at 5 mm intervals in a direction perpendicular to the rolling direction RD. In this case, at least one virtual line VL has, among a plurality of intersections VP between the virtual line VL and the plurality of magnetic domain control treatment lines 11, a maximum distance (dmax) in the rolling direction RD between adjacent intersections (d1 to d7) exceeds 20 mm, and the average magnetic domain width measured along the virtual line VL is 600 μm or less, or a maximum magnetic domain width is 1200 μm or less. Furthermore, this magnetic domain control treatment wire 11 is a tensile stress introduction wire into which a tensile stress of 40 MPa or more has been introduced. As will be described later, the grain-oriented electrical steel sheet according to this embodiment may have a forsterite coating and / or an insulating coating on the surface of the steel sheet that becomes the base steel sheet. Each of these will be explained below. However, when the grain-oriented electrical steel sheet has a base steel sheet and a forsterite coating and / or an insulating coating, the following specifications regarding the chemical composition, magnetic domain control treatment wire, intersection spacing, and magnetic domain width apply to the base steel sheet. However, the specifications regarding the sheet thickness apply to the entire grain-oriented electrical steel sheet, including the base steel sheet and the forsterite coating and / or the insulating coating.

[0013] [Grain-oriented electrical steel sheet] (Chemical composition) The chemical composition of the grain-oriented electrical steel sheet 1 is not limited, and may be the same as that of a known grain-oriented electrical steel sheet 1. For example, the grain-oriented electrical steel sheet 1 has the following chemical composition, in mass %, Si: 2.50 to 7.00%, Mn: 0 to 1.00%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.300%, Cu: 0 to 0.400%, P: 0 to 0.500%, Sn: 0 to 0.300%, and Sb: 0 to 0.012%. 300%, Ni: 0-1.000%, S: 0-0.015%, Se: 0-0.015%, Bi: 0-0.020%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, B: 0-0.080%, and Ti: 0-0.015%. The balance of the chemical composition includes Fe and impurities.

[0014] The chemical composition of the grain-oriented electrical steel sheet 1 may be measured by a general steel analysis method. For example, the chemical components may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, a test piece is obtained from the center of the sample in the thickness direction, and the chemical composition of the grain-oriented electrical steel sheet 1 is measured using a measuring device such as an ICPS-8100 manufactured by Shimadzu Corporation under conditions based on a pre-created calibration curve. The contents of C and S, which are difficult to measure using ICP-AES, may be measured using a combustion-infrared absorption method. The N content may be measured using an inert gas fusion-thermal conductivity method.

[0015] If a forsterite coating and / or an insulating coating is formed on the grain-oriented electrical steel sheet 1, the forsterite coating and / or the insulating coating can be removed from the grain-oriented electrical steel sheet 1 before analyzing the chemical composition of the grain-oriented electrical steel sheet 1 (i.e., the chemical composition of the base steel sheet). The insulating coating can be removed, for example, by immersing the sample in a sodium hydroxide solution, followed by dilute sulfuric acid and nitric acid. The temperature and concentration of the sodium hydroxide, dilute sulfuric acid, and nitric acid solutions, as well as the immersion time, are appropriately adjusted so as not to excessively dissolve the steel substrate of the sample. An example of the conditions for removing the insulating coating is as follows: First, the sample is immersed in a 20% sodium hydroxide solution at 80°C for 15 minutes. The sample is then dried. The sample is then immersed in a 10% dilute sulfuric acid solution at 80°C for 4 minutes. Sludge adhering to the surface of the sample is then removed with a rag or the like. The sample is then immersed in a 10% nitric acid solution at room temperature for approximately 10 seconds while being stirred. The forsterite film can be removed, for example, by immersing the sample in sulfuric acid and then in nitric acid. The conditions, such as the temperature and concentration of the sulfuric acid and nitric acid, and the immersion time, are adjusted appropriately so as not to excessively dissolve the base steel of the sample. An example of the conditions for removing the forsterite film is as follows: First, the sample is immersed in 10% sulfuric acid at 80°C for 3 minutes. Then, the surface of the sample is washed with water using a rag or the like to remove any sludge adhering to the surface. The sample is then dried. Next, the sample is immersed in 10% nitric acid at room temperature for approximately 5 seconds while stirring.

[0016] The thickness of the grain-oriented electrical steel sheet 1 is not limited, but is preferably 0.15 mm to 0.30 mm, for example. By setting the thickness to 0.30 mm or less, classical eddy current loss can be suppressed and iron loss can be further improved. On the other hand, by setting the thickness to 0.15 mm or more, rolling efficiency can be improved, thereby improving productivity.

[0017] (Magnetic Domain Control Processing Lines 11) The multiple magnetic domain control processing lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 function to subdivide the 180° magnetic domains. Subdividing the magnetic domains can reduce the iron loss of the grain-oriented electrical steel sheet 1. A magnetic domain is a collection of magnetic dipoles present inside a ferromagnetic material, and is a small region in which the magnetic moments are aligned in one direction. A 180° magnetic domain is a magnetic domain whose magnetization direction is the <100> orientation of the crystal and is sandwiched between two 180° magnetic domain walls that are approximately parallel to the rolling direction RD. The distance between adjacent domain walls of a 180° magnetic domain (domain wall spacing) is referred to as the width of the 180° magnetic domain. Hereinafter, unless otherwise specified, the width of a 180° magnetic domain will be simply referred to as the "magnetic domain width."

[0018] The extension direction of the magnetic domain control process line 11 is not particularly limited as long as it intersects with the rolling direction (as long as it is not parallel to the rolling direction). The magnetic domain control process line 11 may be substantially perpendicular to the rolling direction RD (substantially parallel to the rolling-perpendicular direction TD). That is, the angle formed by the magnetic domain control process line 11 and the rolling-perpendicular direction TD may be substantially 0°. On the other hand, as exemplified in FIG. 1A , the angle formed by the magnetic domain control process line 11 and the rolling-perpendicular direction TD may be greater than 0°. For example, the angle formed by the magnetic domain control process line 11 and the rolling-perpendicular direction TD may be any value within the range of 0 to 45°. The angle formed by the magnetic domain control process line 11 and the rolling-perpendicular direction TD may be 1° or more, 3° or more, or 5° or more. The angle formed by the magnetic domain control processing line 11 and the direction perpendicular to the rolling direction TD may be 40° or less, 35° or less, or 30° or less.

[0019] 1A , the angles formed by all the magnetic domain control process lines 11 and the direction transverse to rolling TD may be the same. That is, all the magnetic domain control process lines 11 may extend parallel to one another. On the other hand, the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may vary. That is, some or all of the multiple magnetic domain control process lines 11 may extend non-parallel to one another. The average value of the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may be 1° or more, 3° or more, or 5° or more. The average value of the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may be 40° or less, 35° or less, or 30° or less. The average angle can be calculated by measuring the angle between one magnetic domain control treatment line and the transverse direction TD at multiple positions, or by measuring the angles between multiple magnetic domain control treatment lines and the transverse direction TD at one point or multiple positions and calculating the average value. Furthermore, if dmax (the maximum distance in the rolling direction between adjacent intersections of a virtual line and the multiple magnetic domain control treatment lines) is greater than 20 mm, the magnetic domain control treatment lines 11 do not have to be interrupted halfway as shown in Figure 1B (i.e., all of the magnetic domain control treatment lines may be formed across the entire width direction of the steel sheet), and the magnetic domain control treatment lines 11 may include curved portions (i.e., they do not have to be composed of only straight lines) as shown in Figure 1C.

[0020] The type of magnetic domain control treatment wire 11 is not particularly limited as long as it is a tensile stress-introducing wire into which a tensile stress of 40 MPa or more has been introduced, but a suitable example is thermal strain. Thermal strain can be formed using means such as laser irradiation, electron beam irradiation, or ion implantation. The greater the tensile stress, the greater the effect of improving iron loss. On the other hand, the smaller the tensile stress, the better the noise characteristics. The tensile stress can be appropriately selected depending on the characteristics required of the grain-oriented electrical steel sheet 1. The magnitude of the tensile stress is 40 MPa or more in any direction in at least a portion of the magnetic domain control treatment wire 11, preferably 60 MPa or more, and more preferably 80 MPa or more. If the tensile stress in at least one direction is 40 MPa or more, the requirement of "tensile stress in any direction of 40 MPa or more" is satisfied, and the requirement of "multiple magnetic domain control treatment wires are tensile stress-introducing wires into which a tensile stress of 40 MPa or more has been introduced" of this embodiment is considered to be satisfied. Furthermore, for example, it is preferable that the tensile stress in any direction is 300 MPa or less, 200 MPa or less, 180 MPa or less, or 150 MPa or less in at least a part of the magnetic domain control processing line 11. The tensile stress in any direction in the magnetic domain control processing line 11 may be uniform or may vary.

[0021] The magnitude of the tensile stress introduced by thermal strain is measured using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage Corp. The EBSD Wilkinson method is described in detail in A. J. Wilkinson, et al., "High-resolution elastic strain measurement from electron backscatter diffraction patterns: New levels of sensitivity," Ultramicroscopy, Vol. 106, No. 4-5, March 2006, pp. 307-313. When measuring the magnitude of the tensile stress induced by thermal strain using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage, first, the magnetic domain control treatment line 11 is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line 11 and perpendicular to the magnetic domain control treatment line 11. This cut surface is used as the measurement surface. The cross section of the magnetic domain control treatment line 11 included in the measurement surface is analyzed using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage, and tensile stress components in any direction are extracted and their magnitudes are measured. For example, tensile stress components can be extracted in the normal direction ND of the rolling surface, the direction parallel to the magnetic domain control treatment line 11, and the direction perpendicular to the normal direction ND of the rolling surface and the magnetic domain control treatment line 11. The number of measurement points is, for example, 10. If the tensile stress in any direction is 40 MPa or more at at least one point on the grain-oriented electrical steel sheet 1 (i.e., if the tensile stress in at least one direction is 40 MPa or more), the maximum value of the tensile stress in any direction in the multiple magnetic domain control treatment lines of the grain-oriented electrical steel sheet 1 is determined to be 40 MPa or more. Therefore, for the purpose of determining whether the maximum value of tensile stress is 40 MPa or more, the measurement of tensile stress may be stopped when a measurement point where the tensile stress in any direction is 40 MPa or more is found. However, if the σ(TS ｍ ) ２ , T.S. ｍ（β＜２） , or TS ｍ（β≧２） When determining the tensile stress, do not stop the measurement and determine the tensile stress at each measurement point.

[0022] If the magnetic domain control treatment lines 11 are thermally strained, the magnetic domain control treatment lines 11 may not be identifiable visually. In this case, the location of the thermal strain can be identified by photographing a magnetic domain image using an image acquisition device 30 configured as shown in Fig. 4, for example, and observing the photographed magnetic domain image. When photographing, the magnetic domain image is photographed while applying a DC magnetic field along the normal direction ND of the rolled surface of the grain-oriented electrical steel sheet 1, as necessary.

[0023] (Spacing Between Intersections of Imaginary Lines Parallel to the Rolling Direction and Magnetic Domain Control Treatment Lines) (Magnetic Domain Width) As described above, the magnetic domain control treatment lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 function to subdivide 180° magnetic domains. Furthermore, the smaller the spacing between the magnetic domain control treatment lines, the greater the effect of improving iron loss. Therefore, in a typical magnetic domain control treatment, the magnetic domain control treatment lines are formed so that the spacing between them does not exceed 20 mm. In contrast, in the grain-oriented electrical steel sheet according to this embodiment, when a square evaluation area with one side 50 mm long and one side parallel to the rolling direction RD is set on the surface, and when virtual lines VL with a length of 50 mm and parallel to the rolling direction RD are further set within the evaluation area at 5 mm intervals in a direction perpendicular to the rolling direction, in at least one virtual line VL, among multiple intersections VP between the virtual line VL and multiple magnetic domain control treatment lines 11, the maximum spacing in the rolling direction RD between adjacent intersections exceeds 20 mm. That is, in at least some parts, the spacing between the magnetic domain control treatment lines in the rolling direction exceeds 20 mm. FIG. 1A shows, as an example, a state in which only one virtual line VL is drawn. When multiple virtual lines VL are set, a necessary number of other virtual lines can be set parallel to the virtual line VL in FIG. 1A. Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, the virtual lines VL whose maximum spacing in the rolling direction RD exceeds 20 mm satisfy at least one of the following requirements: (1) The average value of the magnetic domain width measured along the virtual line VL is 600 μm or less. (2) The maximum value of the magnetic domain width measured along the virtual line VL is 1200 μm or less. Both the above-mentioned requirements (1) and (2) may be satisfied. That is, the average value of the magnetic domain width measured along the virtual line VL may be 600 μm or less and the maximum value may be 1200 μm or less.

[0024] As described above, while magnetic domain control treatment is effective in reducing iron loss in grain-oriented electrical steel sheets, it also deteriorates the noise characteristics of the grain-oriented electrical steel sheets. Therefore, by reducing the density of magnetic domain control treatment lines, the deterioration of noise characteristics can be suppressed. In other words, both low noise and low iron loss can be achieved in a balanced manner. A maximum spacing between intersections exceeding 20 mm means that there are regions in the steel sheet where the spacing between magnetic domain control treatment lines in the rolling direction exceeds 20 mm, which is more preferable from the perspective of low noise.

[0025] The inventors further investigated and analyzed the changes in magnetic domains before and after magnetic domain control in grain-oriented electrical steel sheets. They found that there are areas where the magnetic domain width is narrowed by magnetic domain control and areas where it is barely narrowed. In other words, they found that the magnetic domain refinement effect of magnetic domain control treatment varies depending on the magnetic domain width before magnetic domain control. More specifically, they found that the magnetic domain refinement effect of magnetic domain control treatment is less likely to be seen in areas where the magnetic domain width is narrow.

[0026] Based on the above findings, it has been found that prioritizing magnetic domain control treatment in regions with wide magnetic domain widths is extremely effective in achieving both low iron loss and low noise. Magnetic domain control treatment in regions with wide magnetic domain widths can reduce iron loss. Since magnetic domain control treatment lines formed in regions with narrow magnetic domain widths are thought to cause deterioration of noise characteristics due to closure domains, minimizing magnetic domain control treatment in regions with narrow magnetic domain widths can prevent deterioration of noise characteristics. Therefore, to minimize deterioration of noise characteristics while achieving iron loss reduction effects, magnetic domain control treatment is primarily performed in regions with wide magnetic domain widths, which have a large magnetic domain refinement effect. While it is preferable to perform magnetic domain control treatment only in regions with wide magnetic domain widths, performing magnetic domain control treatment in regions with narrow magnetic domain widths is acceptable because the deterioration of noise characteristics is small if the proportion is small. Furthermore, while it is preferable to perform magnetic domain control treatment in all regions of the wide magnetic domain width, some regions may not be subjected to magnetic domain control treatment as long as the iron loss reduction effect is sufficient.

[0027] As a result of further investigations into the magnetic domain refinement effect by the present inventors, as shown in FIG. 2 , in regions where the magnetic domain width is approximately 500 μm or less, the magnetic domain width is approximately the same before and after the magnetic domain control treatment. In other words, it is believed that the magnetic domain refinement effect due to the magnetic domain control treatment is hardly obtained in regions where the magnetic domain width is approximately 500 μm or less. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, to obtain a sufficient iron loss reduction effect while reducing the density of the magnetic domain control treatment lines, magnetic domain control is not intentionally performed in such regions where the magnetic domain width is 500 μm or less, and the magnetic domain control treatment lines are formed mainly in regions where the magnetic domain width is greater than 500 μm. As a result, in the grain-oriented electrical steel sheet according to this embodiment, at the imaginary line VL where the maximum spacing in the rolling direction RD exceeds 20 mm, the magnetic domain width measured along the imaginary line has an average value of 600 μm or less, or a maximum value of 1200 μm or less. That is, in the grain-oriented electrical steel sheet 1 that satisfies at least one of the requirements (1) and (2), the magnetic domain width is small across the entire imaginary line VL, thereby achieving a good balance between low noise and low iron loss.

[0028] In the grain-oriented electrical steel sheet according to this embodiment, it is preferable that, in two or more virtual lines VL, the maximum distance in the rolling direction between adjacent intersections VP among the multiple intersections VP exceeds 20 mm, and that at least one of the following requirements is satisfied: (1) The average value of the magnetic domain width measured along each virtual line VL is 600 μm or less; (2) The maximum value of the magnetic domain width measured along each virtual line VL is 1200 μm or less. Both of the above requirements (1) and (2) may be satisfied. That is, the average value of the magnetic domain width measured along the virtual line VL may be 600 μm or less, and the maximum value may be 1200 μm or less. The presence of regions in which the maximum distance between intersections exceeds 20 mm in multiple virtual lines means that there are regions in multiple positions in the steel sheet in which the distance between magnetic domain control treatment lines in the rolling direction exceeds 20 mm, which is more preferable from the viewpoint of low noise.

[0029] More preferably, the average magnetic domain width is 500 μm or less, 450 μm or less, 400 μm or less, 380 μm or less, 350 μm or less, or 300 μm or less, and more preferably, the maximum magnetic domain width is 1000 μm or less, 800 μm or less, 600 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less.

[0030] The rolling direction spacing between the intersections of the virtual line and the multiple magnetic domain control processing lines, and the average and maximum magnetic domain widths measured along the virtual line are determined by the following method. For example, a rectangular sample with both sides measuring 100 mm (or 100 mm or more) can be cut out from the grain-oriented electrical steel sheet 1 and used for measurement. When the grain-oriented electrical steel sheet 1 is a coil, the sample can be taken from any location on the coil. Also, when the grain-oriented electrical steel sheet 1 is used as a component incorporated into an electrical product such as a transformer or motor, the sample can be taken from any location on the component. When the component is small, the length of one side of the sample may be less than 100 mm as long as the length of one side is 50 mm or more. In this case, it is desirable to take the sample by a method such as wire cutting to minimize the influence of mechanical distortion on the sample. A magnetic domain image is acquired from this sample using an image acquisition device equipped with a light source, a magneto-optical sensor (MO sensor), an image sensor, and a signal processing unit. In this magnetic domain image, a square evaluation area is set, each side of which is 50 mm long and parallel to the rolling direction. Furthermore, within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction, are set at 5 mm intervals in a direction perpendicular to the rolling direction. The distances between the intersections of the virtual lines VL and multiple magnetic domain control processing lines 11 are measured, and the maximum value is taken as the maximum distance in the rolling direction between adjacent intersections. The average and maximum domain widths measured along the virtual lines are set using multiple sub-virtual lines that are perpendicular to the sheet surface normal (thickness direction) and perpendicular to the virtual line VL. The sub-virtual lines are 5 mm long and set at 2 mm intervals in the rolling direction. The sub-virtual lines are set so as to intersect with the virtual line VL at their centers. The number of magnetic domains included in each sub-virtual line is measured, and the value obtained by dividing the length of the sub-virtual line by the number of magnetic domains included in the sub-virtual line is regarded as the magnetic domain width on the sub-virtual line. The average magnetic domain width on the sub-imaginary line is the average magnetic domain width measured along the imaginary line, and the maximum magnetic domain width on the sub-imaginary line is the maximum magnetic domain width measured along the imaginary line. That is, in this embodiment, "along the imaginary line VL" means that the centers of the sub-imaginary lines are located at equal intervals on the imaginary line. The locations where the evaluation region and imaginary line VL are set are not limited.The evaluation area and virtual line VL may be set at any location where a virtual line VL can be set so that the maximum distance between adjacent intersections VP in the rolling direction falls within the range of the present disclosure. For example, the virtual line VL may be set so that it passes through an area where no magnetic domain control processing line 11 is provided. On the other hand, if a location where a virtual line VL can be set so that the maximum distance between adjacent intersections falls within the range of the present disclosure cannot be found, it is presumed that the requirements of the present disclosure are not met. Furthermore, this magnetic domain image is output via a cable or wirelessly to an analysis device, which is a computing device such as a personal computer (PC) equipped with a calculation unit, memory, display unit, input unit, and communication I / F. The calculation unit analyzes the magnetic domain structure from the magnetic domain image using a line segment method. An example of measurement using the line segment method will be described. FIG. 3C is a magnetic domain image acquired using a CMOS-MagView manufactured by Matesy GmbH. FIG. 3D is a schematic diagram of FIG. 3C to explain the measurement. In the line segment method, evaluation is performed by drawing line segments Ls perpendicular to the magnetic domains. The line segments are drawn at intervals of three per 1 cm in the rolling direction RD. The magnetic domain width is calculated based on the interval w between the intersections Ip of the 180° domain wall and the line segments Ls. However, if there are closure domains 301 or noise 302, these are not counted as domain walls. Furthermore, when calculating the average magnetic domain width, the average interval is calculated from the length of each line segment Ls and the number of intersections Ip.

[0031] In the grain-oriented electrical steel sheet according to the present disclosure, it is preferable that the maximum value of the tensile stress introduced into the thermal strain, which is an indicator of the strength of the magnetic domain control, in the magnetic domain control treated wire is non-uniform at each measurement point of the tensile stress. The greater the strength of the magnetic domain control, the greater the effect of magnetic domain refinement. However, the greater the strength of the magnetic domain control, the more likely it is that the hysteresis loss will increase and the noise characteristics will deteriorate. According to the new findings of the inventors, the magnetic domain control saturation strength is not uniform in grain-oriented electrical steel sheets. Therefore, it is preferable to make the magnetic domain control strength non-uniform depending on the magnetic domain control saturation strength. The magnetic domain control saturation strength is the magnetic domain control strength at which the effect of the magnetic domain refinement treatment is substantially saturated. When the magnetic domain control strength is equal to or less than the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the reduction in iron loss. However, when the magnetic domain control strength exceeds the magnetic domain control saturation strength, increasing the magnetic domain control strength hardly improves the iron loss reduction effect. On the other hand, even if the magnetic domain control strength exceeds the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the hysteresis loss and the worse the noise characteristics become. Therefore, it is highly preferable that the magnetic domain control strength be set within a range that does not exceed the magnetic domain control saturation strength.

[0032] More preferably, each of a plurality of intersections between the virtual line and a plurality of magnetic domain control treatment lines is defined as a magnetic domain refinement point, and the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points, is defined as TS ｍ , the TS ｍ The variance of σ(TS ｍ ) ２ Then, σ(TS ｍ ) ２ It is a state that satisfies >5.0.

[0033] The "maximum value of tensile stress introduced into thermal strain" is the maximum value of tensile stress measured at an arbitrary measurement cross section. Tensile stress varies across a measurement cross section, and therefore, a single "maximum value of tensile stress introduced into thermal strain" is identified for a measurement cross section. As shown schematically in FIG. 9 , thermal strain 541 has a certain degree of spread across the cross section. The tensile stress is greatest at the location directly irradiated with the laser, and is smaller at locations distant from that location. In other words, the measured value of tensile stress differs for each measurement location on the cross section. Using the tensile stress measurement method described below, the distribution and maximum value of tensile stress across the cross section can be derived.

[0034] When the magnetic domain control strength is uniform, the maximum value of the tensile stress introduced into the thermal strain 541 is a constant value throughout the entire magnetic domain control processing line 11. On the other hand, when the magnetic domain control strength is non-uniform, the maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control processing line is non-uniform for each measurement point of the tensile stress. Hereinafter, the maximum value of the tensile stress introduced into the thermal strain may be simply referred to as "tensile stress."

[0035] The inventors also found that the magnetic domain control saturation strength has a strong correlation with the β angle. The β angle is the angle of deviation from the Goss orientation of the crystal grains around the axis transverse to the rolling direction (TD). The magnetic domain control saturation strength is high where the β angle is small. Furthermore, in grain-oriented electrical steel sheets before magnetic domain control treatment, there is a correlation between the β angle and the magnetic domain width. In grain-oriented electrical steel sheets before magnetic domain control treatment, the larger the β angle, the smaller the magnetic domain width. However, in grain-oriented electrical steel sheets after magnetic domain control treatment, the correlation between the magnetic domain width and the β angle becomes weaker. This is because the magnetic domain control treatment changes the magnetic domain width but does not change the β angle.

[0036] Therefore, it is preferable to select an optimum magnetic domain control strength depending on the magnetic domain width or β angle. For example, it is preferable to perform a magnetic domain refinement process with a high magnetic domain control strength in areas where the magnetic domain width is large and the β angle is small, and to perform a magnetic domain refinement process with a low magnetic domain control strength in areas where the magnetic domain width is small and the β angle is large. Also, as mentioned above, the magnetic domain refinement process is not performed on areas where the original magnetic domain width is narrow. Specifically, the arithmetic mean value of the maximum tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is defined as TS ｍ（β≧２） When this is done, TS ｍ（β＜２） >TS ｍ（β≧２） In this case, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. On the other hand, the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0037] TS ｍ and σ(TS ｍ ) ２ An example of a method for measuring σ(TS) will be described with reference to FIG. 10. The dashed lines in FIG. 10 are multiple imaginary lines VL set at 5 mm intervals in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. The x and o marks in FIG. 10 are intersections of the imaginary lines VL and the thermal strain 541, which is the magnetic domain control treatment line. The β angle at the location marked with an x ​​is 2° or more, and the β angle at the location marked with an o is less than 2°. However, σ(TS ｍ ) ２ In calculating the angle, the β angle at the intersection point does not need to be taken into consideration.

[0038] First, the rolling direction RD of the grain-oriented electrical steel sheet is identified. The rolling direction RD can be identified by the method described below. Next, imaginary lines VL are set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. Then, the intersections of the imaginary lines VL and the thermal distortion 541, which is the magnetic domain control treatment line, are identified. If the thermal distortion 541 cannot be seen with the naked eye, the thermal distortion 541 is identified based on a magnetic domain image. The shape of the sample is preferably a rectangle whose size along the rolling direction RD is 100 mm or more and whose size along the direction transverse to the rolling direction TD is 100 mm or more. One side of the rectangle is preferably parallel to the rolling direction RD.

[0039] Then, TS at all intersections of the measurement area ｍ Measure TS ｍ Variance σ(TS ｍ ) ２ The tensile stress TS introduced in the thermal strain is calculated. ｍ is measured using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage. The EBSD Wilkinson method is described in detail in A. J. Wilkinson, et al., "High-resolution elastic strain measurement from electron backscatter diffraction patterns: New levels of sensitivity," Ultramicroscopy, Vol. 106, No. 4-5, March 2006, pp. 307-313.

[0040] When measuring the magnitude of the tensile stress introduced by thermal strain using the EBSD Wilkinson method and BLG Vantage's Cross Court, first, the thermal strain 541, which is the magnetic domain control treatment line, is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line and perpendicular to the magnetic domain control treatment line. This cut surface is used as the measurement surface. The cross section of the magnetic domain control treatment line included in the measurement surface is analyzed using the EBSD Wilkinson method and BLG Vantage's Cross Court to extract tensile stress components in any direction and measure their magnitude. For example, tensile stress components in the direction normal to the rolling surface, the direction parallel to the magnetic domain control treatment line, and the direction perpendicular to the rolling surface normal and the magnetic domain control treatment line can be extracted. The maximum value TS of the tensile stress identified at each of the multiple measurement points Ｍ Variance σ(TS Ｍ ) ２ is derived in accordance with the method for deriving population variance described in paragraph 2.36 of JIS Z 8101-1:2015 "Statistics - Terms and symbols - Part 1: General statistical terms and terms used in probability."

[0041] Also, TS ｍ（β＜２） and T.S. ｍ（β≧２） is measured by the following method. First, the β angles at the intersections are measured to identify intersections with β angles of 2° or more and intersections with β angles of less than 2°. The β angles of grain-oriented electrical steel sheets are measured by the side reflection Laue method. The side reflection Laue method is widely known as a method for measuring crystal orientation. Next, the maximum tensile stress TS is measured at each of all intersections with β angles of 2° or more. ｍ The arithmetic mean value of these values ​​is calculated. This value is called TS ｍ（β≧２） Furthermore, at each of the intersections where the β angle is less than 2°, the maximum value of the tensile stress TS ｍ The arithmetic mean value of these values ​​is calculated. This value is called TS ｍ（β＜２） The maximum value TS of the tensile stress introduced into the thermal strain 541 at the intersection ｍ The measurement method is as described above.

[0042] Among the multiple magnetic domain control treatment lines 11, the spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 is not particularly limited. The smaller the spacing, the greater the effect of improving iron loss. On the other hand, the larger the spacing, the more improved the noise characteristics. The spacing can be appropriately selected depending on the characteristics required of the grain-oriented electrical steel sheet 1. For example, the spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less. The spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 may be constant or may vary (fluctuate). If there is variation, for example, the average value of the spacing P along the rolling direction RD between adjacent magnetic domain control treatment lines 11 along the rolling direction RD may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The average value of the spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 along the rolling direction RD may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less. The spacing can be determined by drawing one or more straight lines L along the rolling direction RD and measuring the distance between two adjacent points LP at the intersections LP of the straight lines L and the magnetic domain control treatment lines. To calculate the average spacing, multiple measurements of the distance between two adjacent points LP can be taken and the average of the measurements can be calculated. In the grain-oriented electrical steel sheet 1 according to this embodiment, the spacing VP varies along the virtual line VL, which is the measurement position for the magnetic domain width. In other words, even if the average spacing of the magnetic domain control processing lines 11 is within the above range, the virtual line VL, which is the measurement position of the magnetic domain width, passes through an area where the magnetic domain control processing lines 11 are not provided, and therefore the maximum spacing in the rolling direction at the intersection of the virtual line VL and the magnetic domain control processing lines 11 exceeds 20 mm.

[0043] The angle between the magnetic domain control processing line 11 and the direction transverse to the rolling direction TD can be measured using a known angle measuring means after the magnetic domain control processing line 11 and the direction transverse to the rolling direction TD are identified using the procedures described above and below.

[0044] The spacing of the magnetic domain control treatment lines 11 along the rolling direction RD can be measured using a known length measuring means after the magnetic domain control treatment lines 11 and the rolling direction RD have been identified by the procedures described above and below. Here, the spacing of the magnetic domain control treatment lines 11 along the rolling direction RD is the distance from the center of the width of one magnetic domain control treatment line in the rolling direction RD to the center of the width of an adjacent magnetic domain control treatment line in the rolling direction RD.

[0045] (Method for determining the rolling direction RD and the transverse direction TD) The rolling direction RD and the transverse direction (sheet width direction) TD of the grain-oriented electrical steel sheet 1 are determined by the following means. (1) When the sample is cut out from a coil-shaped grain-oriented electrical steel sheet 1, the width direction of the coil is considered to be the transverse direction TD. Also, the direction perpendicular to the transverse direction TD and the normal direction ND to the rolling surface is considered to be the rolling direction RD. (2) When the sample is cut out from a part of an electrical product, etc., the rolling direction RD and the transverse direction TD are determined from the rolling defects on the surface of the grain-oriented electrical steel sheet 1. The extension direction of the rolling defects is considered to be the rolling direction RD. The direction perpendicular to the rolling direction RD and the normal direction ND to the rolling surface is considered to be the transverse direction TD. (3) When it is difficult to identify the rolling direction RD and the direction transverse to the rolling direction TD from the rolling defects on the surface of the grain-oriented electrical steel sheet 1, the rolling direction RD and the direction transverse to the rolling direction TD are identified from the crystal orientation of the grain-oriented electrical steel sheet 1. Specifically, the crystal orientation of the grain-oriented electrical steel sheet 1 to be evaluated is measured at multiple points. Then, the direction in which the angle between the crystal orientation at the measurement point and the direction normal to the rolling surface ND (sheet thickness direction) is closest to a right angle and which has the smallest deviation angle from the axis of easy magnetization <001> is regarded as the rolling direction RD, and the direction perpendicular to the rolling direction RD and the direction normal to the rolling surface ND is regarded as the direction transverse to the rolling direction (sheet width direction) TD.

[0046] (Coating) The grain-oriented electrical steel sheet 1 may have a forsterite coating on its surface (i.e., the grain-oriented electrical steel sheet may be made of a base steel sheet and a forsterite coating formed on the surface of the base steel sheet). The grain-oriented electrical steel sheet 1 may also have an insulating coating on the surface of the base steel sheet or on the surface of the forsterite coating (i.e., the grain-oriented electrical steel sheet may be made of a base steel sheet and a forsterite coating formed on the surface of the base steel sheet and an insulating coating formed on the surface of the forsterite coating, or may be made of a base steel sheet and an insulating coating formed on the surface of the base steel sheet). The forsterite coating and the insulating coating may be formed on one or both sides of the grain-oriented electrical steel sheet 1.

[0047] The forsterite coating is an inorganic coating containing, for example, magnesium silicate as a main component. The forsterite coating is formed, for example, during finish annealing, by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet and the components of the surface of the base steel sheet. The forsterite coating has a composition derived from the components of the annealing separator and the base steel sheet (more specifically, Mg ２ SiO ４ On the other hand, in the final annealing, ２ O ３ When an annealing separator containing mainly SiO 2 is used, the forsterite film may not be formed.

[0048] The insulating coating has the function of imparting electrical insulation and tension to the grain-oriented electrical steel sheet 1. By applying tension to the grain-oriented electrical steel sheet 1 and facilitating domain wall movement in the grain-oriented electrical steel sheet 1, it is possible to reduce iron loss in the grain-oriented electrical steel sheet 1. The insulating coating also provides the grain-oriented electrical steel sheet 1 with various properties such as corrosion resistance, heat resistance, and slip resistance. The insulating coating may be a known coating formed, for example, by applying a coating solution containing phosphate and colloidal silica as main components to the surface of a forsterite coating and baking it.

[0049] [Manufacturing Method] The grain-oriented electrical steel sheet according to this embodiment can achieve the effects described above, regardless of the manufacturing method. However, the following method is preferable because it allows stable manufacturing. That is, the grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps (I) to (III). When the magnetic domain width distribution is clear, such as when the magnetic domain width distribution is estimated by a method other than image acquisition, steps (I) and (II) may be omitted. (I) A magnetic domain image acquisition step of acquiring a magnetic domain image of the grain-oriented electrical steel sheet. (II) A region identification step of identifying regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm based on the magnetic domain image obtained in the magnetic domain image acquisition step. (III) A magnetic domain control treatment line formation step of forming magnetic domain control treatment lines on the surface of the grain-oriented electrical steel sheet after the region identification step. Each step will be described below.

[0050] First, the grain-oriented electrical steel sheet (base sheet) to be subjected to the magnetic domain image acquisition step, or to the magnetic domain control treatment line forming step if the magnetic domain image acquisition step or the region identification step are not performed, may be a known grain-oriented electrical steel sheet. For example, the base sheet may have, in mass %, a chemical composition of Si: 2.50 to 7.00%, Mn: 0 to 1.00%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.300%, Cu: 0 to 0.400%, P: 0 to 0.500%, Sn: 0 to 0.300%, Sb: 0 to 0.300%. %, Ni: 0 to 1.000%, S: 0 to 0.015%, Se: 0 to 0.015%, Bi: 0 to 0.020%, Nb: 0 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0.030%, Ta: 0 to 0.030%, W: 0 to 0.030%, B: 0 to 0.080%, and Ti: 0 to 0.015%. The balance of the chemical composition includes Fe and impurities. The grain-oriented electrical steel sheet used as the base sheet may have a forsterite coating formed on the surface.

[0051] (Magnetic Domain Image Acquisition Process) (Region Identification Process) In the magnetic domain image acquisition process, a magnetic domain image of the surface of the grain-oriented electrical steel sheet is acquired before the magnetic domain control treatment line formation process. In the region identification process, regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm are identified based on the magnetic domain image acquired in the magnetic domain image acquisition process. As described above, the magnetic domain refinement effect is small in regions with small magnetic domain widths, and it is thought that the magnetic domain refinement effect of magnetic domain control is hardly obtained in regions where the magnetic domain width is approximately 500 μm or less. Therefore, it is preferable not to perform magnetic domain control in these regions. In the subsequent magnetic domain treatment line formation process, magnetic domain control treatment is mainly performed in regions where the magnetic domain width exceeds 500 μm, thereby reducing the magnetic domain control treatment lines and reducing iron loss while suppressing deterioration of noise characteristics.

[0052] (Magnetic Domain Control Treatment Line Forming Step) In the magnetic domain control treatment line forming step, magnetic domain control treatment lines are formed mainly in the regions identified in the region identifying step where the magnetic domain width exceeds 500 μm, thereby forming multiple magnetic domain control treatment lines extending in a direction intersecting the rolling direction on the surface of the grain-oriented electrical steel sheet. In this case, the magnetic domain control treatment lines are formed so that there are regions where the spacing in the rolling direction exceeds 20 mm. Examples of methods for this include forming magnetic domain control treatment lines in a direction intersecting the rolling direction at positions more than 20 mm in the rolling direction from adjacent magnetic domain control treatment lines based on the magnetic domain width distribution obtained in the region identifying step, or, as shown in FIG. 1A , forming magnetic domain control treatment lines in a direction intersecting the rolling direction such that, even if the starting point is within 20 mm in the rolling direction from an adjacent magnetic domain control treatment line, no magnetic domain control treatment lines are formed in a partial range, thereby forming magnetic domain control treatment lines so that, at some positions, the spacing between adjacent intersections exceeds 20 mm in the rolling direction.

[0053] Preferably, the magnetic domain control strength is determined according to the magnetic domain width and β angle of the grain-oriented electrical steel sheet before the magnetic domain refinement treatment. The magnetic domain control strength is the amount of thermal strain. In this case, the maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment line becomes non-uniform at each measurement point of the tensile stress.

[0054] The stronger the magnetic domain control strength, the greater the effect of magnetic domain refinement. On the other hand, the stronger the magnetic domain control strength, the more likely it is to lead to increased hysteresis loss and deterioration of noise characteristics. Furthermore, according to new findings by the inventors, the magnetic domain control saturation strength is not uniform in grain-oriented electrical steel sheets.

[0055] The magnetic domain control saturation strength is the magnetic domain control strength at which the effect of the magnetic domain refinement process saturates. When the magnetic domain control strength is equal to or less than the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the reduction in iron loss. However, when the magnetic domain control strength exceeds the magnetic domain control saturation strength, increasing the magnetic domain control strength does not improve the iron loss reduction effect. However, even when the magnetic domain control strength exceeds the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the hysteresis loss and the worse the noise characteristics. Therefore, it is highly preferable to set the magnetic domain control strength within a range that does not exceed the magnetic domain control saturation strength.

[0056] Specifically, it is preferable to perform a magnetic domain refinement process with a high magnetic domain control strength in areas where the magnetic domain width is large and the β angle is small, and to perform a magnetic domain refinement process with a low magnetic domain control strength in areas where the magnetic domain width is small and the β angle is large. In areas where the β angle is large, the magnetic domain control effect is not obtained, so the magnetic domain control saturation strength is 0. In areas where the β angle is below a predetermined value, the magnetic domain control effect is obtained. For example, when the β angle is 2° or less, it is estimated that the magnetic domain control effect is obtained. Furthermore, in areas where the β angle is below a predetermined value, the larger the β angle, the greater the magnetic domain control saturation strength. Furthermore, in areas where the β angle is even smaller, the magnetic domain control saturation strength is approximately constant.

[0057] FIG. 11 shows a graph that schematically illustrates a method for determining the magnetic domain control strength based on the magnetic domain width. The vertical axis of FIG. 11 represents the magnetic domain control strength, and the horizontal axis represents the magnetic domain width. The solid line in FIG. 11 represents the magnetic domain control saturation strength. In regions where the magnetic domain width is small, the magnetic domain control effect is not obtained, so the magnetic domain control saturation strength is 0. In regions where the magnetic domain width exceeds 500 μm, the magnetic domain control effect is obtained. Furthermore, in regions where the magnetic domain width exceeds 500 μm, the magnetic domain control saturation strength increases as the magnetic domain width increases. Furthermore, in regions where the magnetic domain width exceeds approximately 1200 μm, the magnetic domain control saturation strength is approximately constant.

[0058] FIG. 12 shows a graph that schematically illustrates a method for determining the magnetic domain control strength based on the β angle. The vertical axis of FIG. 12 represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the β angle. The solid line graph in FIG. 12 represents the magnetic domain control saturation strength. In regions where the β angle is large, the magnetic domain control effect is not obtained, so the magnetic domain control saturation strength is 0. In regions where the β angle is below a predetermined value, the magnetic domain control effect is obtained. For example, when the β angle is 2° or less, it is estimated that the magnetic domain control effect is obtained. In regions where the β angle is below a predetermined value, the larger the β angle, the greater the magnetic domain control saturation strength. In regions where the β angle is even smaller, the magnetic domain control saturation strength is approximately constant.

[0059] It is most preferable that the relationship between the magnetic domain width at the location where magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in Figure 11. Alternatively, it is most preferable that the relationship between the β angle at the location where magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in Figure 12. The magnetic domain control saturation strength can be used as a target value for the magnetic domain control strength.

[0060] Furthermore, there is a minimum magnetic domain control strength, which is the minimum strength at which the magnetic domain control effect is exhibited. When magnetic domain control is performed, it is more preferable that the magnetic domain control strength is equal to or greater than the minimum magnetic domain control strength.

[0061] However, the magnetic domain control strength may vary slightly from the target value of the magnetic domain control saturation strength. In Figures 11 and 12, the region that is equal to or greater than the minimum magnetic domain control strength and that is within a certain range from the graph of the magnetic domain control saturation strength is referred to as the target range of the magnetic domain control strength. The magnetic domain control strength and the magnetic domain width of the magnetic domain control target portion are preferably within the shaded region surrounded by the dashed lines in Figures 11 and 12. When the maximum value of the tensile stress introduced into the thermal distortion in the magnetic domain control processing line is made non-uniform for each measurement point of the tensile stress, it is preferable to intentionally change the magnetic domain control strength, and in this case, it is preferable to change it within the shaded region surrounded by the dashed lines. The magnetic domain control strength can be changed by changing the irradiation conditions of the laser or electron beam. Specifically, the power, irradiation time, irradiation interval, etc. of the laser or electron beam can be changed to change the average irradiation energy density per unit area Ua (mJ / mm ２ Even if the above Ua is the same, the thermal strain induced in the steel sheet varies slightly depending on the combination of the laser or electron beam power, irradiation time, irradiation interval, etc.

[0062] The magnetic domain control processing lines may be formed by irradiating with a laser or electron beam under known irradiation conditions.

[0063] The direction in which the magnetic domain control treatment lines are formed (the scanning direction in the case of a laser, etc.) and the spacing of the magnetic domain control treatment lines in the rolling direction RD may be controlled by a known method so as to fall within the range of the grain-oriented electrical steel sheet according to this embodiment described above.

[0064] (Specific methods in the magnetic domain image acquisition process to the magnetic domain control treatment line formation process) Acquiring a magnetic domain image and identifying areas where the magnetic domain width exceeds 500 μm can be performed by the following method. The magnetic domain image can be acquired, for example, by an image acquisition device. Next, the distribution of the widths of the 180° magnetic domains (magnetic domain widths) is derived from the magnetic domain image. The distribution of the magnetic domain widths in the original sheet can be derived, for example, by using an analysis device. Areas where the magnetic domain width is equal to or greater than a predetermined value (for example, greater than approximately 500 μm) are determined to be areas where magnetic domain control treatment should be performed (hereinafter sometimes simply referred to as treatment areas).

[0065] The processing region may be determined by the operator visually observing the magnetic domain image displayed on the display unit of the analysis device.

[0066] 4 shows an example of the hardware configuration of an image acquisition device 30 that acquires magnetic domain images of the original sheet (grain-oriented electrical steel sheet 1 before magnetic domain control processing). The image acquisition device 30 includes a light source unit 31, a magneto-optical sensor (MO sensor 33), an image sensor 35, and a signal processing unit 37.

[0067] The light source unit 31 has a light source made up of a light emitting diode (LED), and irradiates the MO sensor 33 with light having a uniform polarization plane.

[0068] The MO sensor 33 is a device for measuring the magnetic domain structure of a magnetic material. The MO sensor 33 has an observation surface on which the magnetic sample to be measured is placed. Light emitted from the light source unit 31 passes through the interior of the MO sensor 33 and is reflected by the reflective layer. The reflected light passes through the interior of the MO sensor 33 again and is output to the outside of the MO sensor 33. When an original plate, which is a magnetic sample, is placed on the observation surface of the MO sensor 33, a leakage magnetic field corresponding to the direction of spontaneous magnetization of the original plate is generated inside the MO sensor 33. This leakage magnetic field rotates the polarization plane of the reflected light.

[0069] The image sensor 35 is a complementary metal-oxide-semiconductor (CMOS) image sensor. The image sensor 35 forms an image of the reflected light from the MO sensor 33 on its light-receiving surface, performs photoelectric conversion, and outputs the photoelectrically converted analog signal to the signal processing unit 37. By detecting the reflected light with a rotated polarization plane using the image sensor 35, the distribution of the leakage magnetic field can be obtained, and the magnetic domain structure of the original sheet can be clarified.

[0070] The signal processing unit 37 includes an amplifier, an AD converter, a digital signal processor (DSP), etc. The analog signal output from the image sensor 35 is amplified by the amplifier. The analog signal is then converted into a digital signal by the AD converter. This digital signal is subjected to predetermined digital processing using the DSP to generate an image signal. The image signal generated by the signal processing unit 37 is output to an analysis device 40 (see FIG. 5 ) via a cable or wireless communication.

[0071] 5 shows the hardware configuration of an analysis device 40 that analyzes the magnetic domain structure of a master sheet. The analysis device 40 is a computer device such as a personal computer (PC). The analysis device 40 includes a calculation unit 41, a memory 43, a display unit 45, an input unit 47, and a communication I / F 49.

[0072] The calculation unit 41 has a central processing unit (CPU). The calculation unit 41 analyzes the magnetic domain structure from the magnetic domain image of the original sheet in accordance with a program stored in the memory 43. The calculation unit 41 then determines a processing region where magnetic domain control processing is to be applied. The processing executed by the calculation unit 41 will be described in detail later.

[0073] The memory 43 includes a read-only memory (ROM) and a random access memory (RAM). The ROM stores programs executed by the CPU of the calculation unit 41 and data necessary for executing these programs. The programs and data stored in the ROM are loaded into the RAM and executed.

[0074] The memory 43 may include a magnetic memory such as a hard disk drive (HDD) or an optical memory such as an optical disk. Alternatively, the memory 43 may store programs and data in a computer-readable recording medium that is detachable from the analysis device 40. Alternatively, the memory 43 may receive the programs executed by the calculation unit 41 from a network via the communication I / F 49.

[0075] The display unit 45 has a display such as a liquid crystal display (LCD), a plasma display, or an organic electroluminescence (EL) display. The display unit 45 displays an image based on the image signal output from the image acquisition device 30. The display unit 45 also displays the analysis results of the magnetic domain structure by the calculation unit 41.

[0076] The input unit 47 has input devices such as a mouse, a keyboard, etc. The communication I / F 49 is an interface for transmitting and receiving data to and from external devices via a network such as a local area network (LAN), a wide area network (WAN), or the Internet.

[0077] As the calculation unit 41, instead of general-purpose hardware such as a CPU, dedicated hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) specialized for analyzing magnetic domain structures may be adopted.

[0078] 4 and 5 show the case where the image acquisition device 30 and the analysis device 40 are separate devices, a system in which the image acquisition device 30 and the analysis device 40 are integrated may also be employed.

[0079] As a means for introducing thermal strain into the surface of the original sheet, known means such as laser irradiation, electron beam irradiation, ion implantation, etc. The configuration of a laser irradiation device 500 that introduces thermal strain by laser irradiation will be described below.

[0080] 6 shows the configuration of the laser irradiation device 500. The laser irradiation device 500 includes a polygon mirror 501, a light source device 503, a collimator 505, a condenser lens 507, a motor 509, a sensor 511, a control unit 513, and a strip threading device 515.

[0081] The strip threading device 515 threads the original strip in the rolling direction RD.

[0082] The polygon mirror 501 has, for example, a regular polygonal prism shape. A plurality of plane mirrors are provided on each of the plurality of side surfaces constituting the regular polygonal prism-shaped polygon mirror 501. A laser beam LB is emitted from a light source device 503, passes through a collimator 505, and is incident on the plane mirror of the polygon mirror 501 in one direction (horizontal direction) and is reflected by the plane mirror.

[0083] The polygon mirror 501 can be rotated around a rotation axis O1 by being driven by a motor 509. The angle of incidence of the laser beam LB with respect to the plane mirror changes sequentially according to the rotation angle of the polygon mirror 501. This sequentially changes the reflection direction of the laser beam LB, enabling scanning of the surface of the original sheet. The symbol P in Figure 6 represents the interval between adjacent magnetic domain control processing lines 11, i.e., the irradiation pitch of the laser beam LB.

[0084] The light source device 503 outputs a laser beam LB in a predetermined irradiation method (for example, a continuous irradiation method or a pulse irradiation method) under the control of the control unit 513 .

[0085] The condenser lens 507 is provided in the optical path of the laser beam LB reflected from the polygon mirror 501. The condenser lens 507 constitutes a condensing optical system with a predetermined focal length. The laser beam LB reflected from the polygon mirror 501 is condensed onto the surface of the original sheet via the condenser lens 507, thereby introducing thermal distortion into the surface of the original sheet.

[0086] The motor 509 is connected to the polygon mirror 501. The motor 509 drives the polygon mirror 501 to rotate under the control of the control unit 513.

[0087] The sensor 511 is connected to the drive shaft of the motor 509. The sensor 511 detects the rotation angle of the polygon mirror 501 rotated by the motor 509. Furthermore, the sensor 511 outputs a signal indicating the detected rotation angle (hereinafter referred to as a rotation angle signal) to the control unit 513.

[0088] The control unit 513 is made up of a processor. The control unit 513 is connected to the light source device 503, the motor 509, the sensor 511, and the strip threading device 515. The control unit 513 receives a speed signal from the strip threading device 515. The control unit 513 also outputs a signal to the motor 509 to instruct the motor 509 to rotate the polygon mirror 501.

[0089] Furthermore, the control unit 513 controls the power of the laser beam LB output by the light source device 503 to be turned on and off based on a stress application signal representing the processing region and a rotation angle signal output from the sensor 511. When the laser irradiation device 500 is electrically connected to the analysis device 40, the stress application signal is input from the analysis device 40 to the laser irradiation device 500. The stress application signal may be input to the laser irradiation device 500 by an operator.

[0090] Next, an example of a method for determining the processing region will be described in detail. The process for specifying the processing region is executed by the calculation unit 41 of the analysis device 40, for example.

[0091] The calculation unit 41 derives the distribution of the magnetic domain width of the original sheet using, for example, a line segment method, and then determines regions where the magnetic domain width is equal to or greater than a predetermined value (for example, greater than approximately 500 μm) as locations where the magnetic domain control process should be applied preferentially.

[0092] In the line segment method, evaluation is performed by drawing line segments perpendicular to the magnetic domains. The line segments are drawn at intervals of three per centimeter in the direction parallel to the magnetic domains. The magnetic domain width is calculated based on the intervals between the intersections of the 180° domain walls and the line segments.

[0093] FIG. 3A shows an example of the distribution of magnetic domain widths of a grain-oriented electrical steel sheet 1 before magnetic domain control treatment, obtained by further analyzing a magnetic domain image acquired using a CMOS-MagView manufactured by Matesy GmbH using a two-dimensional Fourier transform. FIG. 3B shows the distribution of magnetic domain widths after magnetic domain control treatment was performed on the surface of the grain-oriented electrical steel sheet 1 of FIG. 3A , obtained in a manner similar to that of FIG. 3A . The magnetic domain control treatment here was performed by irradiating the surface with a continuous wave laser in a direction substantially perpendicular to the rolling direction RD. In FIGS. 3A and 3B , the units of values ​​are μm. As an example of analysis using two-dimensional Fourier transform, a method of deriving the distribution of magnetic domain widths using short-term two-dimensional Fourier transform (hereinafter referred to as "ST2DFT"), which is a signal processing method long used in the time-frequency analysis of audio signals, extended to a two-dimensional region, will be described.

[0094] The image (magnetic domain image) represented by the image signal acquired by the image acquisition device 30 is expressed as a data string of two-dimensional coordinates (k-l coordinates) as x(k, l). The magnetic domain image to be analyzed in this embodiment is an image binarized using two types of colors, or an image expressed in three or more gradations (multi-gradation), such as grayscale.

[0095] In order to derive the distribution of magnetic domain widths of the original plate 2, the calculation unit 41 executes the following processes (A-1), (A-2), and (A-3): (A-1) Process of extracting multiple partial regions from the magnetic domain image (A-2) Process of performing ST2DFT (A-3) Process of deriving the distribution of magnetic domain widths The processes A-1 to A-3 will be explained in detail below.

[0096] (A-1) Processing for extracting multiple partial regions from a magnetic domain image In order to extract multiple partial regions from a magnetic domain image and analyze the frequency structure of each partial region, the range in the k direction is set to 0≦k≦N. ｋ -1, and the range in the l direction is 0≦l≦N ｌ -1 is used as the rectangular window function Wa(k, l) (N ｋ and N ｌ(k, l is a natural number). As the window function Wa(k, l), a Hamming window, a Hanning window, a Blackman window, etc. can be applied.

[0097] The observation position in the data sequence x(k, l) of the magnetic domain image is expressed by an index (n, m), and the shift amounts of the window function Wa(k, l) in the k direction and the l direction are respectively expressed as S ｋ and S ｌ When written as (n, m, S ｋ , S ｌ is an integer), and nS is calculated from the magnetic domain image as in equation (1). ｋ ≦k≦nS ｋ +N ｋ -1, mS ｌ ≦l≦mS ｌ +N ｌ Data string x of the partial region cut out from the range of -1 ｎｍ (k-nS ｋ , l-mS ｌ ) is obtained.

[0098]

[0099] Figure 7 shows an example in which partial regions corresponding to the observation positions (n, m) = (1, 1), (2, 2), (3, 3), ..., (P, Q) (P and Q are natural numbers) are cut out from the magnetic domain image G.

[0100] In this embodiment, N which determines the range of the window function Wa(k, l) ｋ and N ｌ are parameters corresponding to the number of pixels in the k direction and the number of pixels in the l direction in the partial region, respectively.

[0101] (A-2) Processing to perform ST2DFT The data sequence of the partial region is x ｎｍ (n', m') = x ｎｍ (k-nS ｋ , l-mS ｌ ) and x ｎｍ When a two-dimensional Fourier transform is performed on (n', m'), a partial Fourier image X(f ｋ , f ｌ , n, m) are obtained.

[0102] where f ｋ and f ｌ is the spatial frequency.

[0103] spatial frequency f ｋ The resolution of Δf ｋ , spatial frequency f ｌ The resolution of Δf ｌ When written as Δf ｋ and Δf ｌ is defined as in equation (3).

[0104] Here, Δk and Δl are the spatial resolutions in the k and l directions, respectively, of the magnetic domain image.

[0105] For example, the data string x of each partial region shown in FIG. ｎｍ (k-nS ｋ , l-mS ｌ ) is subjected to a two-dimensional Fourier transform, a partial Fourier image X(f ｋ , f ｌ , n, m) are obtained.

[0106] (A-3) Processing to derive the distribution of magnetic domain widths Partial Fourier image X(f ｋ , f ｌ , n, m) is obtained, the partial Fourier image X(f ｋ , f ｌ , n, m) ｋ ｍａｘ (n, m) and l component f ｌ ｍａｘ (n, m)) can be obtained. Note that, in deriving the peak position, the region near k=0, l=0 is excluded because it is a portion that is highly dependent on the contrast of the image.

[0107] Then, from the spatial frequency resolution defined by equation (3) and the peak positions of the spots in the partial Fourier image, the distribution L(n, m) of the magnetic domain width is derived as shown in equation (4).

[0108]

[0109] In this way, by using ST2DFT, it is possible to quantitatively derive the distribution L(n, m) of magnetic domain widths while maintaining the position information of the magnetic domain image.

[0110] When the calculation unit 41 derives the magnetic domain width distribution, the calculation unit 41 determines the region where the magnetic domain width is equal to or greater than a predetermined value as the processing region (i.e., the region to which the magnetic domain control processing is applied). The control unit 513 of the laser irradiation device 500 controls the power of the laser beam LB to be on for the processing region, and preferably to be off for regions other than the processing region. This introduces the magnetic domain control processing lines 11 into the processing region of the original sheet. Furthermore, the introduction of the magnetic domain control processing lines 11 is suppressed in other regions.

[0111] The above-described procedure can also be used to obtain a magnetic domain image of the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment. In some cases, the magnetic domain control treatment lines 11 are unclear in the magnetic domain image of the grain-oriented electrical steel sheet 1. In this case, the observation conditions may be adjusted so that the magnetic domain control treatment lines 11 can be clearly seen. For example, the magnetic domain control treatment lines 11 can be made clear by applying a DC magnetic field in the direction perpendicular to the sheet surface (thickness direction) of the grain-oriented electrical steel sheet 1.

[0112] (Insulating Coating Forming Step) When forming an insulating coating on the surface of the grain-oriented electrical steel sheet, an insulating coating forming step may be performed after the finish annealing by forming the insulating coating by a known method. The insulating coating forming step may be performed before or after the magnetic domain control treatment line forming step, as long as it is performed after the finish annealing. However, if the insulating coating is formed before the magnetic domain control treatment line forming step, the insulating coating may peel off from the magnetic domain control treatment line 11, so it is preferable to perform it after the magnetic domain control treatment line forming step. When the insulating coating forming step is performed before the magnetic domain control treatment line forming step, it is preferable to form an insulating coating again on the magnetic domain control treatment line 11 after the magnetic domain control treatment line forming step.

[0113] The effects of the embodiments of the present invention will be explained more specifically using examples. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0114] Example 1 Grain-oriented electrical steel sheets of the same lot, 0.23 mm thick and classified as 23P085 in Table 2 of JIS C 2553:2019 "Grain-oriented electrical steel strip," were used as base sheets. Magnetic domain control treatment was performed on the base sheets to obtain the magnetic domain control treatment line shapes shown in Table 1. The magnetic domain control treatment line shapes A to E and A-2 in the table indicate the following: A: Linear magnetic domain control treatment lines were formed in areas where the magnetic domain width exceeded a predetermined value (500 μm). B: Linear magnetic domain control treatment lines were formed across the entire width of the base sheet. C: Regular dashed magnetic domain control treatment lines were formed. D: Random dashed magnetic domain control treatment lines were formed. E: Magnetic domain control treatment lines were formed at intervals of 4 mm only in areas within ±4 mm from the center of each crystal grain in the rolling direction RD. The radius of curvature of the steel sheet at the position where the crystal grains were present during finish annealing was 250 mm. A-2: A linear magnetic domain control treatment line including a curve was formed in the region where the magnetic domain width exceeded a predetermined value (500 μm). The region where the magnetic domain width exceeded 500 μm was identified by the method described above. The magnetic domain control treatment line was a tensile stress introduction line due to thermal distortion. The magnetic domain control treatment was performed by laser irradiation. During the laser irradiation, the average irradiation energy density Ua (mJ / mm ２ ) at 0.5 to 2.0 mJ / mm ２ The irradiation pitch PL (mm) was changed to 4 mm in all cases. The magnitude of the tensile stress introduced in each magnetic domain control treatment line was measured using the method described above. The tensile stress was measured at 10 points on each magnetic domain control treatment line, and the overall maximum value is listed in Table 2.

[0115] The noise and iron loss of the resulting grain-oriented electrical steel sheets that had been subjected to the magnetic domain control treatment were evaluated and the results are shown in Table 2.

[0116] The noise and iron loss were evaluated as follows. First, a three-phase transformer core was fabricated by laminating 180 grain-oriented electrical steel sheets with a thickness of 0.23 mm. The widths of the legs and yoke of the three-phase transformer core were both 150 mm. The height and width of the outer dimensions of the three-phase transformer core were both 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 60 Hz and an excitation magnetic flux density of 1.8 T.

[0117] To measure the noise, microphones were placed at equal intervals around eight locations around the transformer incorporating the three-phase transformer core. The distance between the transformer and the microphones was 30 cm. The noise measurement results from these microphones were A-weighted corrected and averaged to obtain values, which are listed in Table 2 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheet. Examples with a noise evaluation result of 50.55 dBA or less were determined to be examples in which low noise was achieved. Noise evaluation results that were determined to be unacceptable are underlined.

[0118] The iron loss was determined by measuring the voltage and current on the primary and secondary sides with a power analyzer when excitation was performed at a frequency of 60 Hz and an excitation magnetic flux density of 1.8 T, as described above. The determined iron loss is shown in Table 2 as the iron loss evaluation results (unit: W / kg) of the grain-oriented electrical steel sheet. Examples with an iron loss evaluation result of 1.360 W / kg or less were determined to be examples in which low iron loss had been achieved. Noise evaluation results that were determined to be unacceptable are underlined.

[0119] Furthermore, a rectangular sample with both sides measuring 100 mm was cut from a three-phase transformer core for measuring noise and iron loss. A square evaluation area with one side 50 mm long and one side parallel to the rolling direction was set in this rectangular sample. Within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction, were set at 5 mm intervals in a direction perpendicular to the rolling direction. There were nine virtual lines. For each of the nine virtual lines VL, the maximum distance between adjacent intersections in the rolling direction (intersection distance), the average magnetic domain width measured along the virtual line, and the maximum magnetic domain width measured along the virtual line were measured as described above. Table 1 shows the number of virtual lines with a maximum intersection distance exceeding 20 mm, and the number of virtual lines with a maximum intersection distance exceeding 20 mm for which the average and maximum magnetic domain widths were equal to or less than a predetermined value.

[0120]

[0121]

[0122] As can be seen from Tables 1 and 2, when magnetic domain control treatment lines were formed as tensile stress-introduced lines in which a tensile stress of 40 MPa or more was introduced in regions where the magnetic domain width exceeded a predetermined value (500 μm) (Samples Nos. 1 to 15, 20, and 21), the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line exceeded 20 mm for at least one virtual line, and the average magnetic domain width measured along the virtual line was 600 μm or less, or the maximum magnetic domain width measured along the virtual line was 1200 μm or less. As a result, iron loss was low and noise was also low. In contrast, when the magnetic domain control treatment lines were regularly or randomly broken, the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line, or the average and maximum magnetic domain widths measured along the virtual line, were outside the ranges of the present invention. As a result, either or both of the iron loss characteristics and noise characteristics are poor.

[0123] (Example 2) Grain-oriented electrical steel sheets of the same lot with a thickness of 0.23 mm, classified as 23P085 in Table 2 of JIS C 2553:2019 "Grain-oriented electrical steel strip," were used as base sheets. The base sheets were subjected to magnetic domain control treatment so as to have the shapes of magnetic domain control treatment lines shown in Table 3. Here, the shapes of magnetic domain control treatment lines A-3 to A-6 in the table indicate the following: A-3: Average irradiation energy density Ua of 0.75 to 1.75 mJ / mm ２ A-4: The average irradiation energy density Ua was changed within the range of 0.5 to 2.0 mJ / mm ２ A-5: The average irradiation energy density Ua was changed within the range of 0.75 to 1.75 mJ / mm ２ A-6: The average irradiation energy density Ua was changed within the range of 0.5 to 2.0 mJ / mm ２ The magnetic domain control strength was adjusted as described with reference to FIGS. 10 to 12.

[0124] The resulting uniformity of the maximum tensile stress, σ(TSm) ２ , TSm （β＜２） , TSm （β＜２） was measured by the method described above, and the results are shown in Table 4.

[0125] The noise and iron loss of the grain-oriented electrical steel sheets thus obtained that had been subjected to the magnetic domain control treatment were evaluated in the same manner as in Example 1, and the results are shown in Table 5.

[0126]

[0127]

[0128]

[0129] As can be seen from Tables 3 to 5, in all examples, iron loss was low and noise was also small. ｍ ) ２ >5.0 and TS ｍ（β＜２） >TS ｍ（β≧２） When one or both of the above conditions are satisfied, the iron loss is lower or the noise is reduced.

[0130] According to the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces low noise when used in electrical products (excellent noise characteristics), and a method for manufacturing the same, which is therefore highly industrially applicable.

[0131] REFERENCE SIGNS LIST 1 Grain-oriented electrical steel sheet 11 Magnetic domain control treatment line (tensile stress introduction line) RD Rolling direction TD Direction perpendicular to rolling (sheet width direction) ND Rolling surface normal direction VL Virtual line VP Intersection 30 Image acquisition device 31 Light source unit 33 MO sensor 35 Image sensor 37 Signal processing unit 40 Analysis device 41 Calculation unit 43 Memory 45 Display unit 47 Input unit 49 Communication I / F 301 Closure domain 302 Noise Ls Line segment Ip Intersection 500 Laser irradiation device 501 Polygon mirror 503 Light source device 505 Collimator 507 Condenser lens 509 Motor 511 Sensor 513 Control unit 515 Sheet threading device

Claims

1. A grain-oriented electrical steel sheet comprising: a surface having a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction; a square evaluation area having one side 50 mm long and parallel to the rolling direction set on the surface; and imaginary lines 50 mm long and parallel to the rolling direction set within the evaluation area at intervals of 5 mm in a direction perpendicular to the rolling direction; wherein, in at least one of the imaginary lines, among a plurality of intersections between the imaginary line and the plurality of magnetic domain control treatment lines, the maximum distance in the rolling direction between adjacent intersections exceeds 20 mm and the average magnetic domain width measured along the imaginary line is 600 μm or less; and the plurality of magnetic domain control treatment lines are tensile stress introduction lines into which a tensile stress of 40 MPa or more has been introduced.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the average value of the magnetic domain width measured along the imaginary line is 500 μm or less.

3. The grain-oriented electrical steel sheet according to claim 1, wherein, for each of two or more imaginary lines in which the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line is 600 μm or less.

4. The grain-oriented electrical steel sheet according to claim 3, wherein, for each of two or more imaginary lines in which the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line is 500 μm or less.

5. A grain-oriented electrical steel sheet comprising: a surface having a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction; a square evaluation area having one side 50 mm long and parallel to the rolling direction set on the surface; and imaginary lines 50 mm long and parallel to the rolling direction set within the evaluation area at intervals of 5 mm in a direction perpendicular to the rolling direction; wherein, in at least one of the imaginary lines, the maximum distance in the rolling direction between adjacent intersections of the imaginary line and the plurality of magnetic domain control processing lines exceeds 20 mm, and the maximum magnetic domain width measured along the imaginary line is 1200 μm or less.

6. The grain-oriented electrical steel sheet according to claim 5, wherein the maximum value of the magnetic domain width measured along the imaginary line is 800 μm or less.

7. The grain-oriented electrical steel sheet according to claim 5, wherein, for each of two or more imaginary lines in which the maximum value of the interval in the rolling direction exceeds 20 mm, the maximum value of the magnetic domain width measured along the imaginary line is 1,200 μm or less.

8. The grain-oriented electrical steel sheet according to claim 7, wherein, for each of two or more imaginary lines in which the maximum value of the spacing in the rolling direction exceeds 20 mm, the maximum value of the magnetic domain width measured along the imaginary line is 800 μm or less.

9. The grain-oriented electrical steel sheet according to any one of claims 1 to 8, wherein the plurality of magnetic domain control treatment lines are thermally strained.

10. The grain-oriented electrical steel sheet according to claim 9, characterized in that the maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment wire is non-uniform for each measurement point of the tensile stress.

11. Each of the multiple intersections between the virtual line and the multiple magnetic domain control processing lines is defined as a magnetic domain refinement point, and the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points, is defined as TS ｍ , the TS ｍ The variance of σ(TS ｍ ) ２ Then, σ(TS ｍ ) ２ The grain-oriented electrical steel sheet according to claim 10, wherein the grain-oriented electrical steel sheet satisfies a tensile strength of 0.01 to 0.01%.

12. When each of the multiple intersections between the virtual line and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, the arithmetic average value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, which is measured at each of the magnetic domain subdivision points having a β angle of less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, which is measured at each of the magnetic domain refinement points where the β angle is 2° or more, is defined as TS ｍ（β≧２） When this is done, TS ｍ（β＜２） >T.S. ｍ（β≧２） The grain-oriented electrical steel sheet according to claim 10, wherein 13. The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points having a β angle of less than 2°, is defined as TS. ｍ（β＜２） The arithmetic mean value of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, which is measured at each of the magnetic domain refinement points where the β angle is 2° or more, is defined as TS ｍ（β≧２） When this is done, TS ｍ（β＜２） >T.S. ｍ（β≧２） The grain-oriented electrical steel sheet according to claim 11, wherein the following is satisfied:

14. A method for manufacturing grain-oriented electromagnetic steel sheet according to any one of claims 1 to 8, comprising: a magnetic domain image acquisition step of acquiring a magnetic domain image of a surface of the grain-oriented electromagnetic steel sheet; a region identification step of identifying a region in the grain-oriented electromagnetic steel sheet where the magnetic domain width exceeds 500 μm based on the magnetic domain image acquired in the magnetic domain image acquisition step; and a magnetic domain control treatment line forming step of forming a magnetic domain control treatment line on the surface of the grain-oriented electromagnetic steel sheet after the region identification step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed in the region where the magnetic domain width exceeds 500 μm.

15. A method for producing grain-oriented electrical steel sheet as set forth in claim 14, characterized in that in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed by irradiating with a laser or an electron beam.

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